For ordinary automobiles, a window glass can be moved up or down by rotating a window regulator handle. In an attempt to eliminate this cumbersome rotating operation, various automatic, or motor-driven, window regulator devices have been recently discussed, and some of them have been put into practical use.
A kind of such automatic window regulator devices has been disclosed in Japanese Patent Publication No. 42130/1979. FIG. 5 is an electric circuit diagram of this disclosed device, which is shown to have a battery 1 installed in an automobile, an ignition switch 2, a brush-shifting reversible motor 3, a movable switching element 4, a contact 5 for manual operation to lower a window, a contact 6 for one-touch operation to lower the window, a contact 7 for manual operation to elevate the window, a contact 8 for one-touch operation to elevate the window, a control circuit 9 for controlling the rotation of the motor 3, a holding circuit 10 for the lowering operation, a holding circuit 11 for the elevating operation, a voltage detector circuit 12, a relay 13 for the lowering operation, and a relay 14 for the elevating operation.
In the prior art electric circuit described above, when the contact 8 is contacted momentarily, a signal is produced to bring a transistor Tr.sub.4 into conduction and, at the same time, to cause another transistor Tr.sub.3 to conduct. Thus, a relay coil L.sub.2 is energized via a relay contact P.sub.2. This condition of energization is maintained by the circuit, so that the motor 3 is also kept energized, thereby gradually elevating a window glass (not shown) until it bears on the window frame or a foreign object is held between the glass and the frame, in which case the rotational frequency changes. This change is detected by the detector circuit 12, and the resulting signal carries the transistor Tr.sub.4 out of conduction. Simultaneously, the transistor Tr.sub.3 also ceases to conduct. Then, the coil L.sub.2 is deenergized to thereby stop the motor 3.
If the one-touch contact 8 for elevating operation should be held closed for some reason or other, then the relay coil L.sub.2 will be maintained energized by the battery 1 via the movable element 4 and the contact 8. Under this condition, the motor 3 keeps rotating whether the voltage detector circuit 12 delivers the aforementioned output signal or not. Especially, when the neck or an arm of a person is sandwiched between the window glass and the frame, a dangerous situation takes place. Similar condition will arise when the contact 7 for manual operation to elevate the window is kept closed. In this way, a satisfactory safety means is not incorporated in the system.